Priming is a class of ubiquitous behavioral phenomena defined as progressive increase in the speed and strength of behavioral responses to repeated stimuli. Priming has a clear mnemonic component, i.e., responses remain potentiated for a considerable period of time. Thus priming is a simple form of memory. The long-range goal of our research is to determine how priming is initially established, and how it is maintained. Our studies will be conducted in a well-characterized circuit, which generates biting behavior. Experimental advantages of our system include its simplicity, extensive information on the synaptic organization, neurotransmitters and neuromodulators that are present in key circuit elements. Our preliminary data leads us to propose the following hypothesis: Priming is a system-level phenomenon that arises as a result of the interaction between two competing processes, those that actively suppress responses and those that facilitate them. We propose that responses to the initial presentation of the stimulus are actively suppressed. As the stimulus is repeatedly presented, these response-suppressing processes weaken or are surmounted by the response-facilitating processes, ultimately giving rise to the progressive strengthening and speeding-up of the responses. Our preliminary data implicate several neuropeptides act as mediators of these progressive changes in both the response-facilitating and response-suppressing processes. Slow time course of effects of these neuropeptides implicates them in the maintenance of the primed state. We propose to test this model in a series of interdisciplinary experiments that include electrophysiological, biochemical, molecular, and morphological techniques. The general importance of this type of research is likely to extend beyond the specific findings that we obtain because the general mechanisms that underlie motor priming are likely to operate in other contexts. Pathologies in priming mechanisms may be involved in attention disorders, learning disabilities and drug addiction.